1. Field of the Invention
The present invention relates to the creation of mirrors for ring laser gyros and more particularly to the deposition of materials to create the mirrors.
2. Description of the Prior Art
Mirror characteristics are very important in the operation of ring laser gyros. It is important in ring laser gyros to maintain the intensity of the laser beams in the ring laser gyro. The intensity of the laser beams can depend on the characteristics of the mirrors and will remain strong if the mirrors are highly reflective. Further, by utilizing highly reflective mirrors, the ring laser gyro can operate more efficiently by saving excessive power that may be required in keeping the laser beams strong. Mirror characteristics are largely governed by the orientation of the substrate with the respect to material deposited on the substrate. If the orientation of the material on the mirrors is correctly aligned, the light beams may reflect with all their intensity and laser beams will not be weakened. As mentioned before, this would reduce the power necessary to operate the gyro.
To fabricate ring laser gyro mirrors, known deposition techniques are used to deposit material onto substrates in a coating chamber. Deposition sources exist in a coating chamber. High energy electrons are emitted from the deposition sources and strike a target material. The target material is then evaporated onto mirror substrates that exist above the target material. However, during the deposition, the target material is deposited at high angles. High angles are referenced with 0 degrees at the normal to the surface of the mirror substrate. As mentioned before, it is highly important that the orientation be such that mirrors are coated with orientations that will provide optimal mirror characteristics to keep the laser beam intensity in the ring laser gyro.
Deposition of material at high angles results in mirrors with high offset, loss and scatter. In the RLG, it is desirable for a light beam to reflect perfectly wherein the intensity of the beam is maintained and the beam is reflected at the same angle as its incoming angle or incidence angle. Generally, some part of the beams do not reflect properly and some of the original beam reflects at undesirable angles. This is commonly referred to as scatter.
Sometimes it is necessary to create partially reflective mirrors in which some of the original beam to be transmitted through the mirror while the remainder is to be reflected. However, some of the light beam desired to be transmitted through the material on the mirrors is instead absorbed by the material on the mirrors. Absorbed light gives off energy or heat which results in the loss of these photons. This phenomena is commonly referred to as loss. Scatter is also considered a part of loss.
Offset is the amount of uneven stress on a mirror substrate. In mirrors, stresses exist in multiple directions at fight angles. If the stresses are equal, they cancel each other out and no offset exists. If no stresses exist, then of course no offset exists. However, if the stresses are unequal, offset exists causing losses in the mirror. More specifically, when a light beam strikes the mirror, the light beam loses some of its energy. This is a problem because it is desirable to keep the beams strong and not lose any energy.
To reduce offset, loss and scatter, it would be beneficial to prevent material from being deposited at high angles. Consequently, the laser beam in the ring laser gyro would remain strong and the ting laser gyro would operate more efficiently by requiring less energy.